1. Field of the Invention
The present invention relates to a servo circuit which switches between speed control and position control for positioning a magnetic head in a magnetic disk apparatus to a target position. More particularly, the present invention relates to a method and system which automatically adjusts various portions of a servo circuit.
2. Description of the Related Art
In a magnetic disk apparatus, a magnetic head (servo head) is moved in the radial direction of a magnetic disk by a voice coil motor (drive source) in what is called a seek operation. A servo circuit is used for this seek operation to realize a high speed of operation and high precision of positioning. To enable the servo circuit to display its full performance, it is necessary to adjust various portions of the servo circuit before factory shipment, during maintenance and inspection, etc. For example, any differences in the core width of the servo head cause differences in the slope of the position signal, which makes uniform servo control difficult. It is necessary to adjust the core width so as to adjust the detection sensitivity of the position signal and thus maintain a desired slope of the position signal.
Further, differences often arise between the access time during seek operations in the forward direction and in the reverse direction. It is necessary to make the access times match.
In addition, any offset in the analog circuits of the position control system make smooth position control impossible, so it is necessary to eliminate the offset.
The gains of the servo circuit also have to be adjusted. In particular, it is necessary to suitably adjust the speed detection gain of the speed detection circuit to achieve optimal access times and position control.
Also, problems arise when performing the seek operation without synchronization with an index signal on the servo surface. That is, adjustments have been performed by repeatedly performing a seek operation while giving various adjustment values and finding the optimum adjustment values by trial and error. Therefore, when the measurement positions differ in the seek operations, there is a large difference in the measurement values due to differing track positions on the servo surface, etc., and measurement for accurate adjustment becomes difficult.